1. Field of the Invention
The present invention relates to the preparation of titanium dioxide, TiO.sub.2, and, more especially, to the preparation of anatase titanium dioxide devoid of sulfur contaminants and readily dispersible in aqueous solutions.
This invention also relates to the use of such titanium dioxide in the synthesis of alkaline earth metal titanates suitable for electronic applications.
2. Description of the Prior Art
It is known to this art that the alkaline earth metal titanates (principally barium and strontium titanates) which are suitable for electronic applications (production of capacitors, resistors, etc.) must be of high purity, in particular vis-a-vis the sulfur content thereof (&lt;500 ppm).
FR 2,551,743 describes a process for the preparation of alkaline earth metal titanates wherein a titanium dioxide sol is mixed with a solution of a nitrate of the alkaline earth metal, and the resulting mixture is dried and ultimately calcined.
However, the initial sol used in the aforesaid process is obtained by the thermohydrolysis of a titanium oxysulfate, TiOSO.sub.4, such that even after successive and lengthy washings of the sol, not insubstantial amounts of sulfur remain associated with the titanium dioxide and, consequently, such contaminant is transferred into the final titanate powders.
It is also known to the art that it is possible to prepare titanium dioxide devoid of sulfur values by the thermohydrolysis of a solution of titanium oxychloride, but the resulting oxide is essentially completely in rutile form, such that it cannot be used for the preparation of stable sols of TiO.sub.2.